The present invention relates to an optical module that accommodates therein a photosemiconductor device for use in optical communication, and to an optical transmission apparatus using the optical module.
Optical transmission apparatus uses a semiconductor laser and/or photodiodes to transmit/receive light.
Laser modules containing a semiconductor laser device are briefly described below.
In optical transmission apparatus, the light emitted from a semiconductor laser device needs to be efficiently introduced into and coupled to a fiber. The semiconductor laser device is mounted in a hermetically sealed condition in a package made primarily of a metal. For example, the container described in Japanese Patent Laid-Open No. Hei 11-74395 has a frame body formed of any of a metal, an insulator, or a compound material thereof, a first bottom plate fixed to the frame body, and a second metallic bottom plate fixed to the first bottom plate.
In a known configuration for implementing signal transmission at a rate exceeding 10 Gbits/s, as in the related example disclosed in, for example, Japanese Patent Laid-Open No. 2004-40257, the signal to be modulated is transmitted to the interior of a package by using a high-frequency connector provided at the input section of the package in order to receive this signal from the exterior of the package, and the connector is connected to a semiconductor laser device via the transmission line and bonding wire of the substrate formed inside the package.
For internal connection of the package, a cooling element (e.g., a Peltier element) is used to ensure constant characteristics of the semiconductor laser device. More specifically, the configuration using the packaging substrate side of the semiconductor laser device as a cooling plane, and the frame side of the package as a heat-dissipation plane, is used to cool the semiconductor laser device. For this reason, the route from the high-frequency connector (heat sink) on the wall surface of the package to the packaging substrate side (cooler) of the semiconductor laser device needs to be thermally separated. As shown in, for example, Japanese Patent Laid-Open No. 2004-79989 or Japanese Patent Laid-Open No. Hei 11-87852, a configuration is known that uses wire bonding (or the like) to connect the packaging substrate of a cooling element and the substrate mounted on the inner wall of the package.
Laser modules have been described above. It is also known, however, that even in the photodiode module containing a photodiode, the packaging substrate to be connected to a high-frequency connector, and the packaging substrate with a photodiode device mounted thereon are connected using wire bonding. Additionally, it is known that the packaging substrate to be connected to a high-frequency connector, and the packaging substrate with a photodiode device mounted thereon are fixed to a package housing by using independent conductors.
In recent years, there are increasingly growing needs for even-higher-frequency applications exceeding 40 GHz. Accordingly, the improvement of high-frequency connectors for optical module input and output signals of wider frequency bands is being accelerated. At the same time, however, the problem is occurring that depending on the mounting status of the optical module in the package, 40 Gbits/s signal transmission is impeded.
Hermetic sealing packages for accommodating semiconductor laser devices typically use a metal conductor excellent in heat-sinking performance and/or in hermetic sealing weldability, such as iron-nickel-cobalt (Fe—Ni—Co), iron-nickel (Fe—Ni), or copper-tungsten (CuW). Also, these packages usually measure about 5 to 10 mm in height in order to allow for mounting in an optical transmission apparatus. The housing of such a size has come to be seen that wire-bonded sections and other discontinuous sections of a low electric-field containment level suffer resonance in a cavity due to the electric field.